Recently, as a technique of improving communication quality by increasing robustness for frequency selective fading, for example, the OFDM (Orthogonal Frequency Division Multiplexing) scheme and MC-CDMA (Multi Carrier-Code Division Multiple Access) scheme have attracted attention.
In a multicarrier communication scheme, although a signal is transmitted using a plurality of subcarriers with different frequencies, when phases of modulated signals of subcarriers are the same, significant peak power may be provided by combining these signals. When a signal with significant peak power is amplified, the dynamic range is wide and, consequently, an amplifier providing a high linearity is needed for amplifying the signal. However, realizing the amplifier with high linearity is quite difficult while a high efficiency is maintained. Therefore, in a multicarrier communication scheme, there is a problem of reducing peak power.
Up till now, as a method of suppressing peak power in a multicarrier communication scheme, clipping processing of cutting peak components forcibly has been studied. For example, Patent Document 1 discloses extracting a peak component with greater power than a threshold from a multicarrier signal and limiting the amplitude of this peak component. Generally, the likelihood of peak power occurring decreases exponentially according to power, and, consequently, the effect of error characteristics improved by an increase of effective transmission power is greater than the effect of error characteristics degraded by clipping distortion. Thus, according to this method, peak components are subject to amplitude limit, which causes clipping distortion, and, as a result, error characteristics deteriorate. However, power components lower than a threshold are not subject to clipping and are amplified without distortion, so that effective transmission power is increased and the effect of improved error characteristics is yielded.
Patent Document 1: Japanese Patent Application Laid-Open No. HEI 7-46219